1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine and a printer that is provided with a function of forming an image on a sheet.
2. Description of Related Art
Conventionally, as an image forming apparatus of this kind, there is known an image forming apparatus in which a roller pair that is usually called a registration roller pair is arranged on the upstream side of a photosensitive drum acting as image forming means, the registration roller pair being axially supported rotatably on front and behind side plates of an apparatus main body.
The role of the registration roller pair is to temporarily stop a sheet, which is forwarded from sheet supporting means for containing sheets such as a cassette, at a nip portion, correct tip skew of the sheet (skew feeding correction) and adjust timing such that the tip of the sheet fits on an image position of a rotating photosensitive drum to forward the sheet. A roller pressure (pressing force of the roller) of the registration roller pair is required to be set high (approximately 2 kg or more) for correcting skew feeding and, moreover, a clutch such as an electromagnetic clutch for turning on and off transmission of a driving force from a driving source is required to be provided coaxially with the registration roller pair in order to temporarily stop a sheet. Thus, it is a general practice to attach the registration roller pair to front and rear side plates having a large strength in order to bear a high roller pressure and support a heavy clutch.
However, in case of the conventional structure, if paper jamming occurs, when a sheet is in the state in which it is slightly bit by the registration roller pair, since the jammed sheet cannot be seen behind the front side plate even if a transferring portion is opened, jam processing is difficult. In addition, if the image forming apparatus is structured such that the transferring portion is opened together with the registration roller pair, since the clutch is located coaxially, a swinging gear or the like is used for a method of transmitting a driving force. Thus, it is likely that a structure of a driving force transmitting system becomes so complicated that efficiency of transmitting a driving force is reduced, whereby a sheet conveying property declines.
In addition, there is known a system for opening a roller on the driven side of the registration roller pair while holding a roller on the driving side on the main body side. However, since a roller pressure of the registration roller pair is high as described above, a high strength is required for a frame member for supporting a transferring portion and the registration roller pair. Thus, there are inconveniences in that a pressurizing force for lifting the frame increases and, furthermore, alignment of the registration roller pair tends to be collapsed because the registration roller pair is opened.
The present invention has been devised in order to solve the above-mentioned subjects of the prior art, and it is an object of the present invention to provide an image forming apparatus that improves a jam processing property in a transferring portion and is excellent in quality and reliability.
In order to achieve the above-mentioned object, according to the present invention, there is provided an image forming apparatus including: an image bearing member; first conveying means for conveying a sheet along a conveying path; transferring means, which is provided opposing the image bearing member across the conveying path, for transferring a toner image formed on the image bearing member to a sheet to be conveyed by the first conveying means; second conveying means, which is provided between the first conveying means and the transferring means, for conveying a recording material to be conveyed from the first conveying means to the transferring means; and holding means for holding the second conveying means and the transferring means, in which the holding means is capable of opening the conveying path between the transferring means and the image bearing member.